Magnetic recording media disks having hubs (hereinafter hubbed disks) generally consist of three elements: a flexible magnetic recording medium, a flanged metal hub, and an adhesive which secures the medium to the flange of the hub.
The medium is an annular ring made of flexible magnetic sheet material having a thickness of approximately 0.075 mm. The hubs used in hubbed disks may be stamped from a metal sheet or molded from a thermoplastic with a magnetic insert. The hub has a center portion and a recessed flange portion. The center portion fits through the central aperture in the medium, the medium resting on the flange portion, with an adhesive therebetween bonding the medium to the flange.
The distance between the top surface of the medium and the plane of the top of the central portion of the hub must be precisely controlled in order for the head of the digital recording and reproducing equipment to accurately read and record on the medium. This distance will hereinafter be referred to as the distance .alpha.. The present proposed industry standard for the distance .alpha. is 1.36 mm.+-.0.10 mm (American National Standards Institute--European Computer Manufacturers Association/International Standards Organization, hereinafter ANSI-ECMA/ISO, proposed standard). This relatively large allowable deviation for .alpha. is insufficient for optimal head performance, but present manufacturing techniques have been unable to improve upon this tolerance.
The predominant method for the manufacture of hubbed disks is to place a ring of polymer film with a pressure sensitive adhesive coated to both sides, between the medium and hub to secure the medium to the hub. Other types of adhesives may also be used to bond the medium to the hub.
The tolerance of .alpha. is determined by three components: the tolerances of the hub, the adhesive ring, and the process of assembling the disk. Thus, imperfections in the hub, plus imperfections in the adhesive, plus imperfections in the assembly process are additive and all contribute to the currently allowable.+-.0.10 mm.
The deviations in .alpha. can be quantified in two ways. The difference between the maximum and minimum excursion of .alpha. is known in the industry as the total indicated runout (.alpha. T.I.R.). The .alpha. T.I.R. has three components; hub T.I.R., adhesive T.I.R. and assembly T.I.R. If the .alpha.T.I.R. were exactly that of the hub T.I.R. (I.e. total .alpha. tolerance completely due to deviations in the hub) then dividing the .alpha. T.I.R. into the hub T.I.R. would result in a quotient of one. If adhesive and assembly were responsible for additional variance, then the quotient would be less than one. Contrarily, if the adhesive and assembly technique improved the .alpha. T.I.R. relative to the hub T.I.R., then the quotient would be greater than one. Hub T.I.R./.alpha. T.I.R. is hereinafter referred to as T.I.R. ratio. This problem is especially prevalent because of the extreme price competition in this market. With increased cost cutting comes greater deviations in hubs, adhesive and assembly.
Unlike the prior techniques for producing hubbed disks the present invention results in a final product with less deviation than the hub used. The .alpha. T.I.R. of hubbed disks produced under the present invention is actually less than the T.I.R. of the hub used to produce the hubbed disk. Thus, the T.I.R. ratio, hub T.I.R./.alpha. T.I.R. will be greater than one.